APIv4 export action: find DAO by ID instead of just calling the constructor and setting the ID

[jensschuppe]

Overview

Find DAO by ID instead of just calling the constructor and setting the ID. Otherwise, finding references might fail because of missing entity values when comparing, e.g. option_group_id for OptionVaue BAOs.

Before

Running e.g. OptionGroup.export might not work when finding references to option values, because comparing option_group_id will evaluate to null == null here:

civicrm-core/CRM/Core/Reference/OptionValue.php

Lines 43 to 45 in c75c0f2

	if ($targetDao->option_group_id == $this->getTargetOptionGroupId()) {
	return parent::findReferences($targetDao);
	}

After

Comparison with BAO properties will be correct with the BAO being loaded via \CRM_Core_DAO::findById() instead of just calling the constructor and setting the BAO ID.

Technical Details

I'm not sure what might cause that null == null comparison in the first place, in my case it was comparing two unrelated option values that had both option_group_id not set.

[civibot]

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[colemanw]

I think this is fine to merge as it looks more correct than what was there before, and there's decent test coverage.
Even better would be adding a test to cover the bug you experienced.